The marketing of cut flowers and ornamental flowering plants is of considerable economic importance to the horticultural industry. In 1989 the total wholesale United States market for cut flowers and flowering, foliage and bedding plants amounted to approximately 2.43 billion dollars. The sale of cut flowers contributed approximately 459 million dollars to this total, with the sale of potted flowering plants contributing approximately 522 million dollars.
Cut flowers are subjected to considerable stress during harvesting, handling and shipping and their vase life, once in the hands of the consumer, can be shortened considerably due to this stress. Plants produce ethylene, particularly in response to stress, by converting methionine to 1-aminocyclopropane-1-carboxylic acid (known also by the acronym "ACC") and then to ethylene. The enzyme responsible for the conversion of ACC to ethylene is ACC synthase and its activity is known to be inhibited by a number of substances including AVG and AOAA. Ethylene is a gaseous phytohormone produced by plants and flowers and is involved in a number of plant biochemical pathways affecting processes such as abscission, senescence, flowering, fruit setting, fruit ripening, seed germination, sex expression, root growth, internode elongation, epinasty, and geotropism.
A number of formulations are described in the literature and/or are commercially available which aid in extending the vase life of cut flowers. Early formulations employed silver salts, but environmental and toxicity concerns have all but eliminated their use recently. A review of the common ingredients of currently employed formulations for the extension of vase life of cut flowers is provided by A. H. Halevy, et al., Horticultural Reviews, 3: 59-143 (1981).
The ingredients of these formulations typically include one or more sugars which provide an energy source for the cut flowers and one or more antimicrobial agents (believed to prevent clogging, by microbial growth, of the vascular system of the cut flower stems). The prior art teaches that the preferred sugar source for cut flowers is glucose or other so-called "reducing" sugars. Most often, these formulations also include citric acid and/or an acidic inorganic salt, such as aluminum sulfate, to lower the pH of the solution into which the cut flowers are placed to a value around pH 3.5-5.0. Aluminum salts are preferred since it is believed that aluminum ion also plays a role in cut flower preservation by affecting the movement of water in the cut flower stems. Representative of cut flower preservative formulations of this type are those disclosed in British patent specification 2,189,676 to Halo Products Close Corporation which include a nonphytotoxic sugar, a pH buffer comprising a mixture of organic acids, and a germicidal agent.
More recently, cut flower preservative formulations have been disclosed in the literature which contain an inhibitor of ACC synthase such as AVG or AOAA. For example, J. E. Baker, et al., HortScience, 12(1): 38-39 (1977), have reported that immersing the stems of cut carnations (Dianthus caryophyllus L.) in solutions containing L-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid ("AVG"), alone or in combination with antimicrobial agents such as sodium benzoate or propyl gallate, extended their vase life. Similar effects on the extension of the vase life of cut flowers following treatment with AVG have been shown for snapdragons (R. E. Hardenburg, et al., J. Amer. Hort. Soc., 102: 517-520); and for irises, daffodils, and chrysanthemums (C. Y. Wang, et al., Hort. Science, 14: 59-60). J. S. Lee, et al., Han'guk Wonye Hakhoechi (Korean), 31(3): 284-293 (1990, as abstracted in Chem. Abstr., 114(23): 223464c (1991) report that the vase life of Dianthus caryophyllus, variety "White Sim" carnations, was doubled when immersed in distilled water solutions of AOAA. In these instances, the mechanism of action for extension of vase life of the cut flowers has been attributed to the action of AVG in blocking the plant biochemical pathway leading to the production of ethylene.
Typical community well-water supplies are high in hardness and the solutions made up from cut flower preservative formulations containing aluminum salts tend to develop an unsightly turbidity over time due to the formation of aluminum hydroxide flocs or precipitates. Moreover, when these cut flower preservative formulations are acidified by the use of citric acid, microbial growth may occur in the solution with the citric acid serving as a nutrient, leading to unacceptable cloudiness of the solution. If ascorbic acid is employed as the organic acidifying agent, oxidation of the acid causes the development of a yellow color in the solution. In clear cut flower vases, the unsightly cloudiness or yellowing of the water solutions is not acceptable to consumers.
U.S. Pat. No. 5,284,818 discloses stable dry cut flower preservative formulations containing AVG or AOAA, a sugar, aluminum sulfate having from 21 to 27 weight percent water of hydration, and a germicidal agent.